Hello Ralph<
"Please explain your 2nd point a bit more. I have never heard of this."
"2) hold a small hand mirror at the farthest corner of the easel and stop down until you JUST get a full round, clear aperture."
It's just more convenient to hold a mirror and look up into the lens than turning your head. The print will need to 'see' a fully round, clear, unobstructed aperture to be sharp all the way out to the corners. By stopping down until you JUST see a full round aperture, it's at it's widest opening that will still cover the corners, the best compromise setting. This should not be any problem with large prints but can be a bother with small prints OR very short WA lenses. With most modern lenses it should still be in the 'sweet spot'.
Oh, I do disagree with Ctein, 4 element tessar type enlarger lenses should not be avoided, but relished for what they are and can do, softer contrast and definition for portraits. Once you realise that there is a focus shift from f/8 to wide open you can use it to advantage. If you use split-filter printing, you can use split-filter diffusion that is INVISIBLELY DONE but noticeable in the print. Do all of the grade 5 printing at f/8 - 11 and half of the grade 0 printing. Now open the lens and do the second half of grade 0. Adjust the grade 0 percentage to adjust the diffusion.
(grain focus at f/8 then open the lens and see what happens.)
Have fun with it.